In accordance with the improvement of the responsiveness of a power element (for instance, MOSFET) mounted on a motor driver or a power circuit and the like, a steep change of voltage or electric current tends to occur in the switching operation to drive the power element. The power element is a voltage control element for controlling the electric power and the voltage. MOSFET is an abbreviation for metal-oxide-semiconductor field-effect transistor.
The steep change of voltage or electric current causes generation of noise, which might cause malfunction of other components or the product. Therefore, it is required to control the voltage and the electric current so as to change moderately.
Patent Literature 1 and Patent Literature 2 propose noise suppression method.
The method of Patent Literature 1 is that electric potential information of an output terminal is compared with a reference value, and based on the compared result, a switching operation of a transistor is controlled according to a control signal output from a delay circuit after the predetermined time has passed. By this operation, after the predetermined time has passed, a slew rate of output waveform can be maintained within a certain range.
In this method, if the predetermined time (for instance, 1 micro second) is longer than a target time (for instance, 100 nanoseconds) of the slew rate of output waveform, after the predetermined time has passed, the output waveform has already risen. Therefore, the method of Patent Literature 1 cannot regulate the slew rate of output waveform.
The method of Patent Literature 2 is that a phase difference between the slew rate of a delay signal of an output signal that is delayed with a predetermined time and the slew rate of the output signal is detected, and an electric current driving force of an output buffer is regulated according to the detected signal.
Patent Literature 2 describes that the slew rate of the output signal can be regulated by regulating the delay circuit. However, a specific method to regulate the delay circuit (for instance, a calculation method of regulation quantity) is not disclosed. Accordingly, the slew rate of the output signal cannot be regulated to a target slew rate using the method of Patent Literature 2.